Freeform fabrication techniques are particularly usefull for reducing the design, production and maintenance cycle times associated with the manufacture of three-dimensional objects. In the design phase, freeform fabrication techniques are especially useful for prototyping design concepts, investigating inconsistencies in the design, and modifying the design prior to full-scale production. In addition, freeform fabrication techniques have been shown to produce higher quality products at lower cost.
However, the need presently exists for improved freeform fabrication techniques capable of producing complex structures at low cost with minimum set-up and run-time. Many recent techniques, especially in the area of complex metal structures, have been developed but remain mostly inadequate. See e.g. J. J. Beaman, J. W. Barlow, D. L. Bourell, R. H. Crawford, H. L. Marcus and K. P. McAlea, "Solid Freeform Fabrication: A New Direction in Manufacturing," ch. 2 (Kluwer Academic, Norwell, Mass. 1997).
For example, drop generators have been developed and applied to freeform fabrication of three-dimensional objects. See P. F. Jacobs, Rapid Prototyping and Manufacturing, ch. 16 (Society of Manufacturing Engineers, Dearborn, Mich. 1992). With a conventional drop generator, molten metal is ejected as a uniform laminar liquid jet from a fixed-diameter circular injector, or nozzle, located at the bottom of a heated reservoir. The liquid jet is broken into a series of uniform drops of desired size by selecting a fixed injector diameter and varying the frequency of external oscillation near the injector or nozzle orifice. The uniform drops are then deposited in layers on a substrate surface whereupon they solidify to form the desired three-dimensional metal product.
As such, conventional drop generators are used to manufacture metal products having fine, equiaxed micro-structures without manufacturing defects such as porosity or alloy segregation. See C.-A. Chen, P. Acquaviva, J.-H. Chun and T. Ando, "Effects of Droplet Thermal State on Deposit Microstructure in Spray Forming", Scripta Materiala, vol. 34, pp. 689-696 (1996); J.-H. Chun and T. Ando, "Thermal Modeling of Deposit Solidification in Uniform Droplet Spray Forming," Proceedings of the 1996 NSF Design and Manufacturing Grantees Conference, pp. 353-354 (Society of Manufacturing Engineers 1996). Conventional drop generators thus make possible rapid metal forming that does not require expensive and time-consuming post-processing of metal products.
However, despite these advantages, the manufacturing capabilities of conventional drop generators remain overly slow and restricted due to the fixed injector diameters and the relatively small range of possible drop sizes resulting therefrom. For example, in U.S. Pat. No. 5,266,098, Chun et al. disclose a conventional drop generator having a fixed diameter injector that is suitable only for spray forming and metal coating. The Chun et al. drop generator utilizes a laminar circular jet that is excited at a given frequency to break the liquid jet into a series of uniform spherical liquid droplets, which in turn solidify into solid spherical droplets. The fixed-diameter nozzle, for the most part, determines the size of the droplets, and thus relatively small fixed-diameter droplets are formed having a very limited range of possible sizes. As such, the total mass flow rate of the Chun et al. drop generator is inadequate or too slow for large-scale manufacturing and for freeform fabrication of complex and highly detailed three-dimensional objects.
Consequently, a greater variability in droplet sizes is desired to allow more efficient rapid prototyping by allowing the mass flux to be set according to the outline geometry and desired internal micro-structure of the three-dimensional object at a given point.
Recently, in U.S. application Ser. No. 09/010,923, Tseng et al. have disclosed an apparatus for freeform fabrication that utilizes circular and planar jet techniques to form complex three-dimensional objects. A first embodiment of the Tseng et al. invention utilizes a variable-diameter circular liquid jet formed by a conical nozzle, and a second embodiment utilizes a fixed-size laminar planar jet formed by a planar nozzle and external excitation to form uniform rows of droplets. The embodiment utilizing the variable-diameter circular jet is better suited for precision drop deposition since the size and mass flux of the droplets are more precisely controlled according to the specific outline geometry and desired internal micro-structure of the three-dimensional object. On the other hand, the embodiment utilizing the laminar planar jet is better suited for high-speed multiple-droplet deposition of large liquid metal sheets.
However, to further increase the efficiency of freeform fabrication processes, a need still remains for conventional drop deposition systems that selectively deposit droplets only where the desired three-dimensional object is to be formed. With such a system, three-dimensional objects can be formed at a higher degree of resolution, with greater precision and with minimal waste, and without sacrificing speed and efficiency.
Therefore, a principal object of the present invention is to provide an apparatus and method for forming three-dimensional objects wherein materials are selectively deposited in an incremental manner.
Another object of the present invention is to provide an apparatus and method for forming three-dimensional objects wherein unwanted materials are separated from materials to be used to form the three-dimensional objects.
Another object of the present invention is to provide an apparatus and method for forming three-dimensional objects wherein unused materials are deflected and recycled for later use.
Another object of the present invention is to provide an apparatus and method for forming three-dimensional objects wherein selected droplets of molten materials emanate from variable-diameter circular liquid jets.
Still another object of the present invention is to provide an apparatus and method for forming three-dimensional objects wherein selected droplets of molten materials emanate from fixed-size laminar planar jets.
Yet another object of the present invention is to provide an apparatus and method for forming three-dimensional objects wherein selected droplets of molten materials emanate from variable-size laminar planar jets.
Still another object of the present invention is to provide an apparatus and method for manufacturing high quality three-dimensional objects at low cost with minimum setup and run-times.
Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the invention.